This invention relates to a sheet control apparatus and method for sheet-fed stackers and particularly to a sheet retard apparatus and method to positively control the first sheet in a stack to permit movement of a stacker support into stacking position.
In the processing of flexible sheet members formed of paper, film or the like, a continuous series of sheets are formed and fed through a processing line. The individual sheets are often assembled at the end of the line in a vertical stack of a predetermined number of sheets. In a well known process, the successive sheets are discharged into a vertical stacker with each sheet dropping on top of the preceeding sheet in the stack. After a predetermined number of sheets are placed in the stack, the stack of sheets is removed and a new stack is initiated. To permit continuous flow of the sheets and thereby of the processing line, a mechanism must be provided to temporarily support the first sheet in the next stack, or sheets must be diverted into alternate sheet receiving devices. In systems using an in-line receiving device, a temporary support is interposed between the last sheet in a formed stack and the first sheet of the new stack to permit continuous flow of the sheets. The temporary support is advantageously a multiple fork member. The sheets are fed onto the temporary stack support while the formed stack is removed. After removal of the form stacked, the main support structure is returned to its supporting position and in so moving picks up the sheets from the temporary support, which is removed to allow the accumulated sheets to move into the main stacker. The new stack then continues to build until a full stack is established and the system recycles. With high speed processing, the individual sheets are normally formed in a shingled or overlapping manner to create proper timing of the several upstream machines acting to form the final sheets and the stacking machine or apparatus. With high speed systems, the first sheet in a stack tends to move into the stacking receiver with its leading edge dropping into the position of the incoming temporary support. The temporary support is moved as rapidly as possible and thus is moving at a relatively high speed. The leading end of the temporary support such as fork members often engage the first sheet with a possible disruption and damage of the first sheet or sheets. Engagement with the sheet can create for example wrinkles or folds of the sheet tending to interfere with the appropriate formation of a neat and acceptable stack of sheets. This then results at best in a lost or improper product in the stack.